Method and apparatuses for sorting objects in forensic DNA analysis and medical diagnostics

ABSTRACT

The present invention relates to an apparatus and method of sorting objects and identifying the objects in a forensics sample, including using holographic optical trapping to sort objects from contaminants, and performing (single cell) PCR-based STR analysis on the objects to determine their identification. In addition, the chip used as a support for sorting the objects can also be used for performing single cell PCR-based STR analysis. In another embodiment, a microfluidics chip is used to stream the sample and sort the objects, before single cell PCR-based STR analysis is performed. The chip used for sorting utilizing HOT in the absence or presence of microfluidic streaming and sorting can also be the same as that used for the single cell PCR-based STR analysis.

The present application claims priority from U.S. Provisional PatentApplication No. 60/960,059, filed Sep. 13, 2007, the contents of whichare herein incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to methods and apparatuses for sortingobjects in forensic DNA analysis and medical diagnostics. Moreparticularly, the present invention relates to the sorting of sperm fora single cell polymerase chain reaction (PCR) method which is used inforensic DNA analysis, such as STR analysis, to identifypersons/assailants in sexual assault cases. Further, the presentinvention relates to the use of on-chip PCR in forensic DNA analysis.Finally, the present invention of sorting cells and single cell PCR hasapplicability outside of forensics, such as in the field of cancerdiagnostics, where STR-based cell identification is becoming popular todistinguish cancer cells from healthy cells.

2. Description of the Related Art

Conventional forensic DNA specimens are commonly matched to allegedcriminal suspects in modern law enforcement using human identificationsystems involving the amplification of highly polymorphic short tandemrepeats (STRs) by polymerase chain reaction (PCR). PCR is a powerfultool which allows for replicating/amplifying trace amounts of DNAfragments into quantities that can be analyzed in a meaningful way. Thistechnology has been adapted for DNA sequencing, DNA fingerprinting etc.,and has the ability to detect specific DNA fragments in samples.

Thus, forensic DNA analysis is accomplished using the high power ofdiscrimination and rapid analysis speed of STR markers in the humangenome, and has now become the most popular method of choice in forensicDNA analysis.

By way of explanation, STRs are short stretches of DNA that arise when apattern of two to six nucleotides are repeated and the repeatedsequences are adjacent to each other. STR sequences vary in length ofthe repeat unit, number of repeats and in the rigor with which theyconform to an incremental repeat pattern. STR markers are scatteredthroughout the genome and occur as frequently as one every 10,000nucleotides. Based on 2001 International Human Genome SequencingConsortium data, STRs or microsatellites account for approximately 3% ofthe total human genome. Currently 13 STRs are analyzed for humanidentification in forensic analysis, using well-known PCR methods.

Although STR analysis is commonly used, it suffers from severalpitfalls, the most significant of which arises from contamination of thequery DNA samples prior to STR analysis via PCR methods, and the time ittakes to perform the PCR analysis.

For example, the DNA to be analyzed for STRs from sexual assaultevidence should ideally come from the sperm of the assailant. However,the sperm sample is often commonly contaminated with (1) epithelialcells lining the vagina, and occasionally, with (2) epithelial cellsfrom the mouth (buccal cells), and (3) cells from the skin, as well ascells in the urine sample. One might also expect to see erythrocytes,neutrophils, foam cells (non-descript epithelial cells), etc., in sexualassault crime scene samples as well.

Thus, it is clear that better and more accurate STR analysis will beachieved if the sperm cells could be separated from any or all of thecontaminating cells before PCR is performed.

Commonly used methods like differential extraction cannot completelyseparate male (assailant) sperm and female (victim) epithelial cell DNA.For example, initial lysis using reductant free solution, lysesepithelial cells (the most common contaminant in a sexual assaultforensic sample) and leaves sperm cells intact for effective separationof DNA fractions. However, differential lysis often causes immaturesperm cell lysing. Therefore unwanted DNA often gets coamplified duringPCR. This leads to mixed profile and incomplete STR analysis causingmore than 50% of STR analysis based human identification to fail.

In addition, another limitation in solving forensic cases comes from thelimited availability of cells for analysis. This may be due to limitedevidence samples being present, degradation of the DNA and cell samplesin general over time, and/or the presence of very few sperm cells in asexual assault crime sample, to be able to solve the case based onstandard PCR.

Thus, a method that would prevent or alleviate the above problems, andprovide a fast, effective, and reliable method of sorting cells withsingle cell precision in a forensics sample, is desired.

SUMMARY OF THE INVENTION

The present invention relates generally to sorting objects, primarily,at the single cell level, for use in forensics DNA analysis and inmedical diagnostics. More specifically, the present invention relates toa method of sorting and identifying objects in a forensics sample, andincludes providing a holographic optical trapping apparatus for sortingof objects in a forensics sample, the sample which contains objects(wanted and unwanted) to be separated; providing a sample chip(microfluidics-based or otherwise) containing chambers for separation ofthe objects; optically trapping the objects in the forensics sample andsorting them using optical trapping into the wanted and unwantedobjects; removing at least one wanted object from the sample using HOTor microfuidics or both; and performing PCR-based STR analysis on thewanted object to determine their identification.

In one embodiment consistent with the present invention, the wantedobjects are cells, in particular sperm, and the unwanted objects arecontaminants such as epithelial cells, non-sperm objects, etc.

In one embodiment consistent with the present invention, prior to theoptical trapping step, the method further includes providing theforensics sample in a fluidic stream in a microfluidics chamber; andstreaming the sample through the microfluidics chamber. The wantedobjects may be sorted into individual chambers, where single cellPCR-based STR analysis can be performed.

In one embodiment consistent with the present invention, themicrofluidics chamber includes an input chamber which contains theforensic sample, and the sample is streamed into at least one outputchamber, where single cell PCR-based STR analysis can be performed.

In one embodiment consistent with the present invention, a method ofidentifying the objects in a forensics sample and separating themincludes providing a microfluidics chamber having an input chamber andat least one output chamber; providing a forensics sample in the inputchamber, the sample containing objects to be separated; separating theobjects using a microfluidics stream in the microfluidics chamber, intowanted and unwanted objects; removing at least one wanted object fromthe sample into at least one output chamber; and performing PCR-basedSTR analysis on the wanted object to determine an identification of thewanted object.

The performing step of each of the above main embodiments, may beperformed on a single chip, and/or single cell PCR-based STR analysis isperformed in the output chamber.

In one embodiment consistent with the present invention, an apparatusfor sorting objects includes a holographic optical trapping apparatuscontaining a support on which a sample is disposed, the optical trappingapparatus which optically traps and sorts wanted objects from unwantedobjects in the sample; and an apparatus for performing PCR-based STRanalysis on the wanted objects.

In one embodiment consistent with the present invention, the wantedobjects are cells—particularly sperm—and/or single cell PCR-based STRanalysis is performed, and/or is performed on a single chip.

In one embodiment consistent with the present invention, the apparatusfurther includes a microfluidics chip for streaming the sample prior tooptical trapping of the wanted objects.

In one embodiment consistent with the present invention, an apparatusfor sorting objects includes a microfluidics chip containing an inputchamber and at least one output chamber, the input chamber containing asample; wherein the microfluidics chip streams the sample such that thewanted objects are sorted from the unwanted objects in the sample andthe wanted objects are sorted into at least one output chamber; and anapparatus for performing PCR-based STR analysis on the wanted objects.

In another embodiment consistent with the present invention, theapparatus further includes a holographic optical trapping apparatus forsorting the wanted objects from the unwanted objects in the sample, fromthe input chamber into the at least one output chamber.

In another embodiment consistent with the present invention, the wantedobjects are cells—particularly sperm—and the unwanted objects arecontaminants, and a single chip is used to sort the objects and performthe PCR-based STR analysis, and/or the PCR-based STR analysis is singlecell PCR-based STR analysis.

With the present invention, single cell PCR-based STR analysis willresolve sexual assault cases where multiple assailants are involved, andwill provide an opportunity for solving cases where limited material(i.e., a limited number of eluted sperm) is available for bulk(multi-cell PCR-based) forensic analysis to be feasible and reliable.Further, single cell PCR-based STR analysis will resolve the issues ofcontamination (i.e., where epithelial cells of the victim are mixed withthe sperm of the assailant, which causes the DNA of the victim to beco-amplified with the DNA of the assailant). Thus, single cell PCR willsolve the primary cause of STR analysis failure for human identificationby ruling out co-amplification.

The ability to work with few cells (i.e., perform single cell PCR) isimportant in identifying the assailant in a forensic case whichotherwise cannot be solved, and it also enhances the chance of rulingout involvement of incriminated persons where limited samples areavailable (i.e., azospermic males).

Further, single cell PCR improves the speed of processing the sample,since sorting single cell, or rather a few single cells (for statisticalpurposes), takes less time than when dealing with hundreds of cells (asis ordinarily required).

The use of HOT for single cell sorting prior to PCR, lends the presentinvention to the use of disposable chips, which provide a completelysterile environment for sample handling. This will avoid contaminationissues (i.e., from a user/technician handling the sample) on a single ormulti-platform. Thus, one can preserve evidence data in a sterileenvironment for future re-analysis if needed.

Further, by using microfluidic chips, the sample volume to be handled inthe present sorting and identification process, will be largelyminimized. The present invention will also be inexpensive to operate,since smaller volumes of samples imply less reagents are requiredoverall. The present invention is flexible enough to offer differentchoices for cell sorting (i.e., using HOT alone or using microfluidicsalone, or combining both), different modes of cell lysis and DNAextraction (on-chip or in separate tubes), and different modes of PCR(on-chip using a flatbed thermocycler, or in micro-centrifuge tubesusing conventional PCR machines).

Further, with the present invention, both HOT and microfluidics-basedcell sorting are gentle processes and do not cause immature cell lysing.

The present invention does not require sample staining prior to Sampleprocessing (unlike LCM (laser capture micro-dissection) which has thecapability for single cell extraction)—thereby cutting down on the costof dyes and additional sample processing steps. However, the proposedinvention is compatible with fluorescently stained samples, if needed.

Since embodiments of the present invention include a visualization-basedtechnique (i.e., microscopic visualization, or even machine vision inthe event of a completely automated machine), the present inventionoffers better documentation for forensic sample processing, such asrecording all the intermediate steps, and recording the number of cellsbeing analyzed in a given case or documenting the morphology of thecells analyzed.

The present invention is amenable to complete automation, whereasconventional techniques, such as differential extraction, is not.Further, the apparatus can be miniaturized and made portable and samplechips to carry out sorting, and PCR can be made disposable.

Although the present invention described herein for use in forensic DNAanalysis primarily relates to sexual assault cases and focuses on spermseparation, the general method of single cell PCR based STR analysis isextendable to other types of forensic samples where separation of asignificant number of a certain cell type for human identification, maybe a challenge. Since differential extraction relies entirely on achemical process with no microscopic visualization, a technique such asthat of the present invention, that can visualize and extract thecell(s) of interest for STR analysis would be of great benefit to thefield of forensics.

The present invention extends the scope of single or few cell basedforensic DNA analysis beyond sexual assault crime cases to humanidentification of war victims or soldiers (in the realm of militaryforensics, for example). It could also be used for paternity testingwhere, often, collection of enough sample(s) from the suspect is aproblem.

Further, the present invention may be used in areas of cancerdiagnostics where PCR-based STR analysis is often used to distinguishcancerous cells from normal cells in a specimen sample and STR analysisat single cell level will provide additional information about theseverity and progression of the disease by accounting for the percentageof cells in the specimen sample that looks healthy versus cancerous.

There has thus, been outlined, some features consistent with the presentinvention in order that the detailed description thereof that followsmay be better understood, and in order that the present contribution tothe art may be better appreciated. There are, of course, additionalfeatures consistent with the present invention that will be describedbelow and which will form the subject matter of the claims appendedhereto.

In this respect, before explaining at least one embodiment consistentwith the present invention in detail, it is to be understood that theinvention is not limited in its application to the details ofconstruction and to the arrangements of the components set forth in thefollowing description or illustrated in the drawings. Methods andapparatuses consistent with the present invention are capable of otherembodiments and of being practiced and carried out in various ways.Also, it is to be understood that the phraseology and terminologyemployed herein, as well as the abstract included below, are for thepurpose of description and should not be regarded as limiting.

As such, those skilled in the art will appreciate that the concepts uponwhich this disclosure is based may readily be utilized as a basis forthe designing of other structures, methods and systems for carrying outthe different purposes of the present invention. It is important,therefore, that the claims be regarded as including such equivalentconstructions insofar as they do not depart from the spirit and scope ofthe methods and apparatuses consistent with the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic of a holographic optical trapping apparatusaccording to one embodiment consistent with the present invention.

FIG. 2 is a schematic of an object sorting apparatus according to oneembodiment consistent with the present invention, including amicrofluidics chip, a holographic optical trapping apparatus, and anapparatus which performs PCR-based STR analysis.

FIG. 3 is a schematic of an object sorting apparatus according toanother embodiment consistent with the present invention, including amicrofluidics chip, and a single cell PCR/STR apparatus

FIG. 4 is a schematic of an object sorting apparatus according toanother embodiment consistent with the present invention, including amicrofluidics chip, a holographic optical trapping apparatus, and aPCR/STR apparatus.

FIG. 5 is a schematic of an object sorting apparatus according toanother embodiment consistent with the present invention, including amicrofluidics chip, and a PCR/STR apparatus.

FIG. 6 is a schematic of an object sorting apparatus according toanother embodiment consistent with the present invention, including amicrofluidics chip and an on-chip PCR/STR apparatus.

DESCRIPTION OF THE INVENTION

The present invention relates to methods and apparatuses for sortingobjects in forensic DNA analysis. In particular, the present inventionuses a novel approach—namely, single cell PCR-based STR analysis, with(or without) holographic optical trapping (HOT), and/or microfluidicchambers, to separate sperm from contaminants and perform identificationof assailants in forensics DNA analysis. The chip used for the purposeof sorting the objects can also be used to perform the downstream stepsof cell lysis, DNA extraction and PCR (on-chip PCR).

Further, a micrifluidics chip is used to stream the samples and sort theobjects (cells) of interest from unwanted contaminants before performingsingle cell based PCR analysis. Rather than using HOT alone for sorting,the procedure uses microfluidics based sorting prior to using HOT in thecase of samples where a larger number and variety of contaminants arepresent. Such a combination of HOT with microfluidics for sorting mayalso improve throughput (cut down sorting time prior to PCR) and puritywhen compared to using HOT alone for sorting. The chip used for objectidentification and sorting can be the same as the chip meant for singlecell PCR for STR analysis.

Single cell PCR for forensics has several advantages including theability to avoid contamination from unwanted cells, the ability tohandle limited evidentiary samples, ability to detect multipleassailants, improved speed and automation, as well as likely reductionin costs. On-chip PCR for forensic analysis also has multiple advantagessuch as portability, miniaturization, and maintaining a sterileenvironment for handling.

The present invention proposes a novel use of on-chip PCR for forensicanalysis, thereby creating a new kind of disposable chip which wouldminimize intermediate handling. The proposed invention includes avisualization-based method and offers the ability to document all theintermediate processing steps in analyzing a sample.

While the present invention describes details in the light of forensics,the scope goes beyond forensics, such as into the field of cancerdiagnostics, where identifying rare cells (i.e., cancerous cells), anddistinguishing them from normal ones based on STR, is of great value.

In a first embodiment consistent with the present invention,,holographic optical trapping (HOT) is used for identifying and trappingsperm cells, and sorting them from other contaminating cells in a sexualassault crime sample.

The HOT apparatus 100 (see U.S. Pat. No. 6,055,106, to Grier et al., forexample, which is herein incorporated by reference), includes a laser101 which is used as a light source, to optically trap and manipulateobjects in a sample 102 on a support 103 (see FIG. 1). Specifically, thelaser 101 emits a collimated laser beam 104 which is shaped by adiffractive optical element (DOE) 105, such as a spatial light modulator(SLM) 105, and transferred to a back aperture of an objective lens 106via, for example, telescope lenses 107, 108 and dichroic mirror 109. Thebeam 104 is diffracted by the DOE 105 into a plurality of beamlets andforms a plurality of independently movable optical traps 110 on thesupport 103 of a microscope apparatus (of which objective lens 106 is apart). The support 103 and sample 102 are illuminated by the beam 111emitted from a light source 112. The point B′ is conjugate to B inFIG. 1. Note, however, that telescope lenses 107, 108 may be eliminatedfrom the apparatus 100 and replaced with a single transfer lens, ifdesired.

Imaging optics 113, such as a CCD camera, etc., are used to view theoptically trapped objects in the sample 102. The apparatus 100 may beConnected to a computer (not shown) which can control the opticaltrapping and can record the data during operation.

In this embodiment, the holographic optical trapping apparatus is usedto sort objects in a forensics sample 102. The sample 102 of sperm andother cells, is obtained from the crime scene, and the cells in thesample 102 are eluted and placed on a microfluidic chip 200 (see FIG. 2)for example, by pipetting, gravity, or by other active or passivemechanisms. The microfluidic chip 200 is placed on a microscope platform103 for visual inspection—either manual or automated using computercontrol.

Thus, HOT 100 is used to separate the sperm cells in the forensicssample 102, by visual (microscope or monitor) inspection, from othercontaminating cells, by moving the optically trapped sperm from one areaof the microfluidic chip 200 into individual chambers 201-203 on thesame chip 200, for example.

Then, PCR-based STR analysis 204 is performed to identify the person(typically matching the STR signatures stored in the CODIS database)whose DNA signature matches with the STR analysis of the sperm (specimensample). The PCR-based STR analysis is in itself well-known in the artand has been broadly commercialized.

In particular, the chip 200 is placed on a flatbed thermocycler, wherethe extracted DNA is amplified by PCR using STR primers which arecommercially available for forensic cases. Alternatively, acustom-designed appropriate primer can be used where forensic cases arenot involved. The number of thermocycles is increased to leave enoughDNA from the individual cells at the end of the PCR cycling.

DNA extraction may be performed by centrifugation (post cell lysis) orby attaching to magnetic beads, where the DNA is eluted from the beads(magnetic or others), by changing the pH (altering the charge on theDNA, i.e., by affecting binding of the DNA to the beads) or by changingthe salt concentration of the elution buffer.

Once PCR is completed, the amplified DNA is run on gels (typically) forSTR analysis on the amplified DNA that has undergone PCR, where each PCRreaction corresponds to amplified DNA from a single sperm. Commerciallyavailable instruments may be used for this purpose.

Conventionally, a significant number of cells were required to get areliable STR readout signal. However, with the gentle method ofHOT-based sperm separation and improved sensitivity, a more reliableseparation of sperm from contaminating non-sperm cells can be performed,and one can scale down the sample collection in terms of number of spermcells needed for PCR-based STR analysis from about 200 (as is requiredin conventional methods), to a few cells, or even to the level of singlecell PCR—greatly increasing its efficiency (see chambers 201-203).

Thus, single-cell PCR can be carried out on each individual sperm inchambers 201-203, using standard PCR methods (lysing the sperm one at atime, extracting the DNA).

In another embodiment, the DNA after extraction from single cells, canbe transferred to Eppendorf tubes for carrying out PCR reactions priorto STR analysis. Multiple PCR reactions can be carried out at any giventime on one machine. However, to avoid DNA loss during transfer fromsorting chip to tubes, the PCR may be carried out on-chip using flatbedthermocycles as described above.

In addition to standard PCR/STR analysis in tubes or on plates, in oneembodiment, the analysis can also be performed on a single chip 206(on-chip PCR) (see FIG. 3). As shown in FIG. 3, in this embodiment, thesperm in sample 102 can be lysed in situ 200, or the sperm in each wellor chamber 201-203 can by lysed and passed through a filter 207 toseparate the cell debris from the DNA, and only allow DNA to proceed tothe next chamber 208, where PCR (bulk) is run (i.e., on DNA from severalsperm). The chamber 208 is connected to an on-chip PCR device 206 withthe capability of STR readout.

A final STR report is then generated for each individual sperm analyzed,and statistics generated on the STR readouts from individual sperms. Theresulting data is matched with the CODIS database for humanidentification if it is meant for forensic use, for example.

The virtue of individual sperm (single cell) PCR based STR readout isthat, it:

(1) solves the contamination problem in multi-cell situations which iscurrently the major problem in PCR based STR analysis which arises dueto co-amplification of unwanted DNA.

(2) it increases the likelihood of detecting multiple assailants (ifinvolved in a sexual assault case) based on the statistical significanceof the STR readout (well-established by standard regulations);

(3) it offers the ability to analyze those crime cases where obtaining200 sperm cells is a challenge due to the limited availability of samplesperm cells, thus, enhancing the chance of ruling out incriminatedpersons in a sexual assault case, for example; and

(4) It speeds up the total processing time since separating one or a fewcells is faster than separating many more cells used in standard PCRbased analysis.

Thus, one can envision revolutionizing the nature and scope of STR basedforensics offering solutions to more cases where sufficient samplecollection posed a problem before. Analysis on one or few cells will cutdown on sample collection time as well.

In rare cases, where allele dropout is a problem and an STR profile(based on standard bulk PCR analysis) could not be matched to the CODISdatabase (the dominant allele masking the other), there is a greaterlikelihood of matching an STR signature as obtained from single cell PCRto the database with relevant statistical calculations, to arrive at theneeded probability.

By analyzing STR on individual sperm cells and repeating the analysisfor a number of sperm cells from a given sample on a one-by-one basis,one can now reliably solve sexual assault cases where multipleassailants are involved such as in a gang-rape crime. Thus, nodeconvolving is needed in resolving STR profiles of individuals from acell-mixture set.

Further, single-cell PCR based forensics will offer the ability toperform repeat measurements on multiple single cells from a givenspecimen and more statistically reliable data can be obtained in solvinga crime case.

The present invention is also cheaper to operate in microfluidic chipsby reducing the cost of reagent. Further, the use of disposables and thescope for miniaturization of a HOT apparatus will increase itsportability.

Thus, it can be seen that HOT-based sperm sorting is more reliable thanexisting techniques without compromising the amplicon DNA. Further,since HOT 100—which uses light to trap and sort entities of interestfrom a forensic sample 102—is not damaging towards the DNA obtained fromthe cell samples 102, this method would speed up data collection (i.e.,it will take less time to trap one or a few cells than to trap 200cells), result in improved speed (by cutting down on sample size forsingle cell PCR-based forensics), and improved purity (differentialoptical sorting is better than differential lysis which relies onchemical extraction), and provide scope for automation (whichessentially none of the existing techniques for forensic DNA analysiscurrently allow).

The improved purity and quality control of the sperm cells sorted usingHOT 100 will facilitate improved PCR and STR analysis 204, therebyhelping to resolve a plethora of unsolved cases where contamination byepithelial or other cells poses a problem by amplifying unwantedamplicons from contaminating cells (often from the victim) inconjunction with the desired amplicon from sperm (from the assailant).Note PCR and STR analysis can be performed on contaminants or unwantedobjects (i.e., epithelial cells) as well, in order to cross-check thevalidity of a filed criminal charge.

Alternate sperm sorting techniques, such as chemical separationapproaches like differential extraction, or mechanical separation suchas vacuum filtration or trak-etch filtration (which are mechanicallydriven), do not offer visual (microscope based) inspection in spermsorting as does HOT 100, and are not as efficient. These methods oftenresult in immature lysis of sperm and are harmful towards the DNA to beanalyzed for STR readout.

In addition, none of the afore-mentioned existing methods for cellhandling before STR analysis have the ability to perform single cellanalysis which is an advantage of the present invention. Opticaltrapping (HOT) 100 offers the unique ability to visualize and trap spermcells rather than relying on chemical separation approaches wherevisualization based sorting is not possible.

Thus, the present invention uses single or oligo cell PCR for forensics,which will help resolve sexual assault cases typically unsolved bystandard PCR methods. Further, the present invention will resolve caseswhere the perpetrator is, for example, an oligospermic male. Such maleshave very low sperm count in their seminal fluid ejaculate which makesstandard PCR based STR methods fail where the source DNA to be amplifiedcomes from differential lysis. Thus, the use of HOT 100 and single cellPCR 204 can provide the identification sought in forensics analysis.

In a second embodiment consistent with the present invention, amicrofluidic chip 300 having chambers can be used with or without HOT100, to perform the sperm sorting prior to PCR-based STR analysis 301(see FIG. 4).

In particular, the proposed method of sperm sorting can be performed onan optically clear microfluidic chip 300 thereby allowing operations onvery small volume samples. Sample separation using a microfluidic chip300 with chambers is well-known in the art, and have been broadlycommercialized. Here by modulating the idea and incorporating channelsat different layers (in depth or z-direction) in the microfluidic chipoffers single cell separation.

For example, a custom-made microfluidic chip 300 (see FIG. 4) with aninput chamber 304 and multiple output chambers 305 (connected viachannels 306 but which can be isolated from one another following spermsorting), may be used for separating single sperm cells from othercontaminants (non-sperm) in the sample 302, as well as from one another.The microfluidic chamber 300 would include a flow injector, and a flowbuffer (not shown) through the chamber 304.

In one example, the dimensions of the input chamber 304 are Chosen basedon the exact sample 302 needs, but for sperm sorting, estimates could be500 μm length, 100 μm width, and a depth based on the sample volumeused, but probably 1-5 μl (or even less, such as in the range ofnanoliters since on-chip PCR can be successfully carried out innanoliter volume). The output chambers 305 may be smaller than the inputchamber 304, and of an appropriate size, with the chambers 305 beingconnected to the input chamber 304 via one channel 306 or multichannels306, and with one or more chambers 304 connected to the input chamber304 forming a sterile disposable chip.

The use of a microfluidic chip 300, with or without HOT 100, may beimportant in reducing reagent cost and maintaining an optimal numberdensity of sperm before doing PCR-based STR analysis in cases wherelimited starter material is available.

For example, in this embodiment, a swab is obtained from the crimescene, and the sample cells (sperm and contaminants) 302 eluted andplaced on a microfluidic chip 300 via active mechanism or pipetting. Themicrofluidic chip 300 is placed on a microscope platform 303 for visualinspection (manual or automated using computer control) (see FIG. 4).

The microfluidic chamber is then used for separation of sperm fromepithelial cells, and HOT 100 can be used in another embodiment, forsubsequently sorting the sample 302 placed in the input chamber 304 intoindividual chambers 305 (if desired). In particular, since sperm tend tostick to chamber or well 304 edges, it may be easy to increasethroughput (i.e., how many sperm cells can be sorted in a given time),and also avoid interference from contaminating non-sperm cells if thereare more than one output chamber/well 305 of the multiple connectingchannels 306 emanating from the input chamber/well 304. This arrangementwill improve reliability and efficacy in sperm sorting.

After sorting has been performed using microfluidic streaming or byusing HOT 100, the chambers 305 can be sealed off from the input chamber304 using conventional means, such as valves/stoppers. Alternativelybackflow of sorted objects can be prevented by reducing (modulating) thedimension (typically width) of the channels rather than keeping themuniform throughout a given microfluidic chip.

Lysis of sperm in their individual chambers 304 is then performed on themicrofluidics chip 300, and then the lysate can be extracted manually orusing robotics, in order to extract the DNA. DNA from each sperm is thenplaced in a separate chamber 305 either on the same chip 300, or in analternative embodiment, on a second chip, as described in the firstembodiment.

As stated above in the first embodiment, the chip 300 with the extractedDNA is then placed on a PCR (thermocycler) machine 306 for amplificationusing STR primers. STR analysis is then run on the PCR amplified DNA(i.e., run gels to identify bands against standard STR markers).

Thus, single-cell PCR-based STR analysis can be performed in thisembodiment as well.

Finally, as stated above, a final STR report is generated for individualsperm analyses and statistics are generated for appropriate matchingagainst a standard database (e.g., CODIS for human identification).

Thus, as stated above, HOT 100 is used with PCR-based STR analysis, toallow single cell analysis and standard bulk (multi-cell) analysis.Further, as described above, HOT 100 allows individual cells to bemoved, rotated and manipulated in three dimensions. One can use visibleor infrared illumination for optical trapping to identify and move thesperm cells thereby separating them from contaminating epithelial cellsin a sample. Use of visible or infrared excitation light eliminatesmajor concerns of cell damage which may be encountered when using UVlight. The sorted sperm cells can be introduced into a Separate chambereach (i.e., one or a few cells of the same kind in a given chamber) andthe desired PCR-based STR analysis in situ or otherwise, can beperformed.

One can therefore, choose to carry out the subsequent PCR and STRanalysis on single or multiple sperm cells offering all the advantagesof single cell analysis as compared to standard bulk analysis.

As stated above, the PCR-based STR analysis can also be performedon-chip, so that only a single chip is used from start to finish.

In a third embodiment consistent with the present invention, themicrofluidics chip 400 of the second embodiment is modified such thatthe rate of flow of the fluid from the input chamber 401 (see FIG. 5),the channel 402 dimensions (i.e., length, width, depth) and materialsfor the chip 400 itself, are controlled and the flow is adjusted in amanner such that no two cells from sample 402 occupy the same positioninside the channel 403, or more critically, near junction 404, andtherefore, single cells can be sorted through channels 405 into chambers406-409, etc. One chamber (i.e., 406) contains ideally one cell.

In addition, a filter 410 may be incorporated to only allow sperm cellsto enter channel 403.

The cells can be lysed in chambers 406-409 and the correspondingchambers 411-414 will contain the extracted DNA from individual cells.DNA in chambers 411-414 can be PCR'ed 415 on-chip in one embodiment (asdescribed above), or can be transferred to another chip either viapipetting or through active (pumping) mechanisms, or even using roboticarms to carry out the DNA transfer.

In an alternative embodiment, the input chamber 401 containing thesample 402 (cell mixture) eluted from the swab can be constructed in alayered format where sperm cells can be allowed to settle on the bottomof the chamber 401 and can be constructed as emanating from that layer,to draw individual cells through channel 403. The layers containseparate sets of channels and do not allow cell admixture. Valves may beincorporated in the microfluidic chips 400 to prevent backflow of sortedmaterials.

In a fourth embodiment consistent with the present invention, elutedcells from a sample 500 (see FIG. 6)—are eluted into an inlet chamber501 on a microfluidic chip 502, where the sample 500 is deposited.

Contaminants (i.e., epithelial cells) from the sample 500 settle on thebottom of the inlet chamber/reservoir 501 and sperm cells are mobilizedvia fluid flow through channel 503 to collect in outlet chamberreservoir 504. In a second stage, individual collection reservoirs504-507 collect sperm sorted via channel 508, according to previouslydescribed methods.

In a third stage, lysis of individual sperm takes place in chambers509-512, with the extraction of the DNA being accomplished by singlecell PCR (on-chip PCR) according to previously described methods.

In another embodiment, the process of the PCR and STR analysis can beautomated and high speeds can be achieved which will eliminate anotherbottleneck often experienced in the current approaches used in STRanalysis. Currently differential extraction is almost entirely manuallyoperated. Other techniques like mechanical sorting using mesh filters ofvarying pore sizes (trak-etch filtration) are also not conducive toautomation which tends to clog the filters. However, HOT-based sortingof sperm from epithelial cells can be easily automated. Automation willcut down on operation costs and time and thereby solve more sexualassault cases in a given time.

In yet another embodiment consistent with the present invention, themethods proposed are compatible with automation and multiplexing—i.e.,running multiple forensic sample analyses, thereby increasingthroughput.

In yet another embodiment consistent with the present invention,coupling with robotics where multiple crime samples can be eluted,separated and tested at the same time, thereby increasing throughput,includes additional advantages since it is platform independent—i.e.,can be carried out on glass slides (glass coverslips) or in test tubesor in Eppendorfs or even in 96-well format (given that there aremachines now that can do PCR in 96-well or higher-well formats, in situPCR is possible using such separation). Robotic handling avoids othersource of contamination which could arise from operator handling of thecell samples.

As stated above, this methodology is also compatible with in situ PCR onforensic samples. Therefore, all advantages of in situ PCR will be validsuch as to:

(i) reduce chance of contamination since in situ PCR will involve fewersteps and avoid transfer of samples from one container to another; and

(ii) cut down cost of such forensic analysis by limiting supply costthat is likely involved with more steps and transfer of samples.

Thus, due to limited DNA content from a single cell, the number of PCRcycles before STR analysis will be increased as compared to existingmulti-cell (bulk) PCR based methods.

To approach the issue of equal amplification of the 13 STR fragmentsusing genomic DNA as template amplicon from a single sperm, one can runreal time PCR as a control for additional quality control withoutcompromising time or efficiency. Also, multiplex PCR can be performed inthe same way on a single cell as is done with multiple cells.

Thus, single cell PCR based forensics offers additional advantages foranalyzing crime samples without compromising what existing bulk(multiple cell) PCR based forensics offers.

Finally, as stated above, single cell PCR can be automated and can alsobe performed on chip (on-chip PCR) furthering opportunities forminiaturization and portability.

The opportunity for miniaturization and portability opens the scope ofsingle cell PCR based forensic DNA analysis beyond sexual assault crimecases to human identification of war victims or war soldiers (in therealm of military forensics, for example), and even paternity testingwhere, often, collection of enough sample(s) from the suspect is aproblem.

The virtue of individual sperm STR readout is that it increases thelikelihood of detecting multiple assailants (if involved in a sexualassault case) based on the statistical significance of the STR readout(well-established by standard regulations). It also enhances the chanceof ruling out incriminated persons in a sexual assault case wherelimited samples (<200 sperms could be obtained) were available foranalysis. In rare cases, where allele dropout is a problem and an STRprofile (based on standard bulk PCR analysis) could not be matched toCODIS database (the dominant allele masking the other), there is agreater likelihood of matching an STR signature as obtained from singlecell PCR to the database with relevant statistical calculations, toarrive at the needed probability. Thus, the present invention isadvantageous in resolving many problems now existing in forensics DNAanalysis.

It should be emphasized that the above-described embodiments of theinvention are merely possible examples of implementations set forth fora clear understanding of the principles of the invention. Variations andmodifications may be made to the above-described embodiments of theinvention without departing from the spirit and principles of theinvention. All such modifications and variations are intended to beincluded herein within the scope of the invention and protected by thefollowing claims.

1. An apparatus for sorting objects, comprising: a holographic opticaltrapping apparatus, said optical trapping apparatus which opticallytraps and sorts a sample of wanted objects from unwanted objects; amicrofluidics chip containing an input chamber in which said sample isdisposed, for streaming said sample from said input chamber to aplurality of output chambers; wherein said sorting of said sample intosaid wanted objects and said unwanted objects takes place at said inputchamber using said holographic optical trapping apparatus; wherein saidsorting removes said wanted objects individually into each of saidplurality of output chambers, such that each of said output chamberscontains a single wanted object; and an apparatus which performssingle-cell PCR-based STR analysis on each of said single wantedobjects, said apparatus being disposed downstream from said plurality ofoutput chambers.
 2. The apparatus of claim 1, wherein said wantedobjects are cells and said unwanted objects are contaminants.
 3. Theapparatus of claim 1, wherein said wanted objects are normal cells andsaid unwanted objects are cancerous cells or vice versa.
 4. Theapparatus of claim 1, wherein said sorting and said PCR-based STRanalysis are performed on a single microfluidics chip.
 5. The apparatusof claim 1, further comprising: a plurality of valves disposed at saidinput chamber, to prevent backflow.
 6. The apparatus according to claim1, further comprising: a filter disposed at an outlet of said inletchamber.
 7. The apparatus according to claim 1, wherein said sorting andPCR-based STR analysis are automated and multiplexed.
 8. An apparatusfor sorting objects, comprising: a microfluidics chip containing aninput chamber and a plurality of output chambers, said input chambercontaining a sample of wanted objects and unwanted objects to beseparated; wherein said microfluidics chip streams said sample from saidinput chamber into said plurality of output chambers, such that saidwanted objects are sorted from said unwanted objects; wherein saidsorting removes said wanted objects individually into each of saidplurality of output chambers. such that each of said output chamberscontains a single wanted object: and an apparatus which performssingle-cell PCR-based STR analysis on each of said single wantedobjects, said apparatus being disposed downstream from said plurality.9. The apparatus of claim 8, further comprising: a holographic opticaltrapping apparatus which sorts said wanted objects from said unwantedobjects at said input chamber, and removes said wanted objects into saidplurality of output chambers.
 10. The apparatus of claim 8, wherein saidmicrofluidics chip and said apparatus for performing said PCR-based STRanalysis are provided on a single chip.
 11. The apparatus of claim 8,wherein said objects are cells, and said unwanted objects arecontaminants.
 12. The apparatus of claim 8, wherein said wanted objectsare normal cells and said unwanted objects are cancerous cells.
 13. Theapparatus of claim 8, further comprising: a plurality of valves disposedat said input chamber, to prevent backflow.
 14. The apparatus accordingto claim 8, further comprising: a filter disposed at an outlet of saidinlet chamber.
 15. The apparatus according to claim 8, wherein saidsorting and PCR-based STR analysis are automated and multiplexed. 16.The apparatus according to claim 1, wherein said wanted objects aresperm cells.
 17. The apparatus according to claim 8, wherein said wantedobjects are sperm Cells.
 18. The apparatus according to claim 1, whereinstreaming of said sample is controlled such that no two objects fromsaid sample occupy a same position in a channel or at a junction in saidmicrofluidics chip.
 19. The apparatus according to claim 1, wherein saidunwanted objects settle in said input chamber, and said wanted objectsflow to said output chamber.
 20. The apparatus according to claim 1,wherein each of said single wanted objects flows from each of saidindividual output chambers to a corresponding individual lysis chamberwhere said PCR-based STR analysis is performed on each of said singlewanted objects.
 21. The apparatus according to claim 1, wherein saidwanted objects are streamed into a single output chamber prior to beingstreamed into said individual output chambers.
 22. The apparatusaccording to claim 8, wherein streaming of said sample is controlledsuch that no two objects from said sample occupy a same position in achannel or at a junction in said microfluidics chip.
 23. The apparatusaccording to claim 8, wherein said unwanted objects settle in said inputchamber, and said wanted objects flow into said plurality of outputchambers.
 24. The apparatus according to claim 8, wherein each of saidsingle wanted objects flows from each of said individual output chambersto a corresponding individual lysis chamber where said PCR-based STRanalysis is performed on each of said single wanted objects.
 25. Theapparatus according to claim 8, wherein said wanted objects are streamedinto a single output chamber prior to being streamed into saidindividual output chambers.
 26. The apparatus according to claim 1,wherein said microfluidics chip is optically transparent.
 27. Theapparatus according to claim 9, wherein said microfluidics chipisoptically transparent.